The "Just hit your knees" argument asks the non-believer in question to just drop all logic and rationality and to just accept the theist's god into your heart for old times sake. This can go two ways. You can refuse to do it because it's ridiculous (you might as ask Kermit the Frog into your heart), or do it and then nothing will happen. When nothing happens, a common response from theist is that you weren't sincere enough, and weren't really asking god into your heart.

Significance of the Heart

Usually you will be asked to accept the god into your heart. It's questionable why this god would want to be in your blood pumping organ. Theists also tend to use the word "heart" to claim certainty, for example:

I know in my heart.

I feel him in my heart.

But the heart is not for knowing or feeling. Your brain is for knowing things and to feel emotions. Your heart is for pumping blood around your body. So it remains unanswered why would a being require spritiual entry to the heart rather than the brain.